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| Titel |
Seasonal methane dynamics in three temperate grasslands on peat |
| VerfasserIn |
Carolyn-Monika Schäfer, Lars Elsgaard, Ralf Conrad, Søren O. Petersen |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250054044
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| Zusammenfassung |
| Natural peatlands are important sources of atmospheric methane (CH4) due to their
waterlogged, highly organic soils. Approximately 14 % of the European peatland area has
been drained for agriculture, mainly for grasslands. Drainage leads to a strong decrease in
CH4 emissions or may even turn peatlands into CH4 sinks because the anaerobically
produced CH4 can be effectively oxidized in unsaturated soil layers. Maybe as a result of the
small net fluxes observed, below-ground dynamics of CH4 in grasslands on peat have largely
been neglected.
The objective of this study was to investigate seasonal CH4 dynamics of temperate
grasslands under different soil moisture regimes. A former bog with partly well preserved
Sphagnum peat and two fens with highly decomposed peat – one with a high pyrite (FeS2)
content – were chosen as study sites. Groundwater fluctuations were less than 40 cm at the
pyrite-poor fen and ~ 90 cm at the other sites during the course of a year. Fluxes of CH4 were
monitored with closed chambers for one year as part of a project for the determination of
emission factors for managed organic soils in Denmark. In addition, 1-m deep soil CH4
concentration profiles were measured in each of the four meteorological seasons and the
associated archaeal communities assessed via molecular fingerprint (T-RFLP) analysis.
Methanogens were identified by sequencing and phylogenetic analysis of 16S rRNA genes.
For the former bog site, CH4 production potentials were determined in short-term
laboratory incubation experiments at 20 Ë C in parallel to the soil concentration
profiles.
Averaged over all sites, the grasslands were sinks for CH4 with a flux of -4±8 μg CH4
m-2 h-1 (mean ± SE, n = 254), with no apparent seasonality at either site. At the pyrite-rich
fen, CH4 dynamics were suppressed with soil CH4 concentrations never exceeding 15 ppm
and no detection of methanogens. At the other sites, methanogens were detected in all
samples. There were marked differences in archaeal community composition between sites
and peat depths, but not between seasons. Soil CH4 concentrations reached up to 150 and
1000 μmol CH4 dm-3 soil at the pyrite-poor fen and the former bog, respectively. At
the fen, groundwater table seemed to control the concentration profile shapes as
expected. In contrast, at the former bog site the Sphagnum peat’s water holding
capacity and physical structure seemed to reduce the effect of drainage, leading
apparently to CH4 production and accumulation well above the groundwater table. CH4
production potentials were measurable in ~ 40 % of the bog’s peat samples (n
= 98) mainly below 30 cm peat depth, ranging from 0.001 to 0.40 μmol CH4 g
dry peat-1 day-1. Surface peat showed CH4production after a lag phase of 2 – 7
days.
At the pyrite-poor fen and the former bog, the CH4 oxidation zone was large enough to
suppress substantial CH4 emissions. However, aerenchymous plants may create emission
hotspots within these grasslands. This was shown in additional measurements at both
sites on single spots with occurrence of Soft Rush (Juncus effusus). These spots
showed a yearly average CH4emission of 1.07±0.11 (n = 38) and 1.79±0.49 (n = 38)
mg CH4 m-2 h-1 for the bog and the fen, respectively, which is comparable to
annual average emissions from natural European peatlands. The distribution of
aerenchymous plants, the peat’s physical structure and potential capillary fringe
effects should be considered more intensively in the evaluation of grasslands on
peat as potential CH4 emission sites. Also, data on the distribution of methanogens
should be further pursued in these ecosystems to allow interpretations regarding
their influence on soil CH4 concentrations in comparison to environmental factors. |
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